Click here to see what happens when you start your browser and visit the Internet Movie Database at imdb.com.

Each dot in this graph represents a website. The gray dot in the middle is imdb.com; the red dots near it are advertising sites that have created cookies in your browser and are now tracking your behavior on the IMDB.

The advertising sites are colored red because privacychoice.org has determined that they're behavioral tracking sites. But just because a dot isn't red doesn't necessarily mean it's not tracking you.

Hover your mouse over any of the sites to learn more about them.

When you're done, click here to continue your web adventure. Our next stop is the New York Times website.

It looks like the New York Times is affiliated with some of the same advertising companies as the IMDB.

Because the same cookies were transmitted to the same advertisers when you visited both sites, those advertisers effectively track you across them. That's valuable data for their market research.

When you're ready, click here to visit our next stop, the Huffington Post.

Some companies are already using their knowledge about you to determine what you see on the sites they're affiliated with—not just the ads you see, but the actual content you read. Eli Pariser examines what this could mean for society at large in his book The Filter Bubble.

By the way, if the graph is starting to look a bit confusing, try dragging the dots around with your mouse to get a better view.

Then, click here to go to our next stop, gamespot.com.

If you haven't realized it yet, companies are tracking you across most of the sites you visit daily on the web. It's quite likely that these companies know more about you than your government. Some of them might even know more about you than your best friends.

Click here to visit our final stop, reference.com.

Thanks for trying out this demo. If you'd like to see this graph change in real time based on the sites you visit in your own browser, feel free to try the Collusion Firefox add-on. Even visiting the sites mentioned in the demo will probably give you different visualizations, because some services you may be logged into—like Facebook—can also track you across sites.

If you want to block companies from tracking you on the internet, you can install TrackerBlock for Firefox and Internet Explorer.